The present invention concerns methods of inhibiting the burning of natural fibers (e.g., wool, wool fibers, animal hair, cotton), synthetic fibers (e.g., acetate, nylon, polyester, viscose rayon), or blends thereof (e.g., wool/cotton blends), or fabrics or yarns composed of natural fibers, synthetic fibers, or blends thereof, involving treating the fibers (or fabrics or yarns) with polyamic acid or at least one polyimidesiloxane or mixtures of polyamic acid and at least one polyimidesiloxane. In addition, the present invention concerns products produced by such methods.
Wool is natural protein fiber that self-extinguishes when exposed to a flame. Hence wool can be used in applications that require flame-resistance. Wool is used in airplane interiors, such as seat covers, sidewall panels, and carpets, and fabrics used in pillow covers and blankets. Wool is also a preferred fiber for uniforms worn by military personnel because of its comfort properties such as high moisture regain.
Wool may have to be made flame proof to be used in certain applications such as protective clothing worn while handling molten metals, apparel worn by racecar drivers, and aircraft interiors. Wool fabrics can be made to resist burning by blending with fibers such as Aramid (Nomex™ and Kevlar™) or chemical treatment of wool. Disadvantages of blending with Aramid include poor abrasion resistance, difficulty in dyeing, poor UV and light resistance, higher rates of heat release, and higher cost. Conventional chemical treatments to confer flame resistance to wool include treatment with the flame retarding agents applied to cotton, such as salts of borate, phosphate, metals, and tetrakishydroxymethyl phosphonium, and titanium compounds. Zirconium complexes under the trademark Zirpro™, issued by the International Wool Secretariat, are one of the successful flame retardants for wool. Many modifications of the Zirpro™ process according to specific needs have been made. For example, tetrabromophthalic acid (TBPA) is used along with Zirpro™ to obtain low heat release wool. However, zirconium salts have the environmental disadvantage of zirconium being a heavy metal.
Properties of wool such as easy dyeability, inherent resistance to burning, warmth, and resilience make it a preferred fiber even today. Zirpro™ is the only commercially available flame retardant treatment method for wool. However, heavy metals salts are used in the process and not all compounds required for the treatment are easily available. Hence an alternative treatment to make wool flame proof is needed.